Controllable ferrite phase shifter having means to cool the ferrite



Sept. 5, 1967 w p. CLARK 3,340,483

CONTROLLABLE FERRITE PHASE SHIFTER HAVING MEANS TO COOL THE FERRITE Filed Nov. 30, 1965 5 Sheets-Sheet 1 [sum z #44455 JW/Ff/Olilf) 22% 4. 5y M4 /A/l4 P. CAM/z,

Arrow 1y Sept. 5,1967 w p CLARK 3,340,483

CONTROLLABLE FERiRIT E PHASE SHIFTER HAVING MEANS TO COOL THE FERRITE Filed Nov. 30, 1965 5 Sheets-Sheet 2 COOLAA/T 6004/1/10 Arrazwsl Sept. 5, 1967 w. P. CLARK 3,340,483

CONTROLLABLE FERRITE PHASE SHIFTER HAVING MEANS TO COOL THE FERRITE Filed Nov. 30, 1965 S Sheets-Sheet 5 United States Patent 3,340,483 CONTROLLABLE FERRITE PHASE SHIFTER HAV- ING MEANS T0 COOL THE FERRITE William P. Clark, Orange, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware 1 Filed Nov. 30, 1965, Ser. No. 510,611

8 Claims. (Cl. 333-31) ABSTRACT OF THE DISCLOSURE An improved microwave ferrite phase shifter having increased power handling capability. The phase shifter is characterized by a unique structure which allows a liquid coolant to circulate around the ferrite element. The structure makes use of a closed dielectric support member functioning in the triple capacity of: a liquid-tight container for the coolant; a mechanical support for the ferrite element; and a dielectric load for the ferrite element.

This invention relates to microwave devices and, more particularly, to an improved ferrite phase shifter of microwave energy.

Various devices have been developed to provide proper phase shifting of microwave or RF (radio frequency) energy propagating in elements of phased antenna arrays. In large phased array systems, the complexity of controlling the RF phase shifting can be greatly reduced by providing RF phase shifting at the inputs to rows, columns, or subarrays of the antenna element phase shifters. However, this can only be accomplished with an RF phase shifter capable of handling high peak and average power, since the unit must be able to carry all the power that is distributed to each of the rows, columns, or subarrays to which it is connected.

Among the recently developed RF phase shifting devices is a ferrite phase shifter which is capable of providing substantial phase changes per unit length by electrical means. Basically the device consists of a ferrite rod centrally located inside a waveguide section, with an external longitudinally applied magnetic field being used to control or vary the desired phase shift. The device, though providing desired phase shifts with relatively low magnetic fields, is limited by the peak power which it is capable of handling, as well as by the average deliverable power. Therefore, it cannot be used at the inputs to rows, columns, or subarrays in a phased array system, so as to reduce the phase shifting complexity therein.

Accordingly, it is an object of the present invention to provide an improved ferrite phase shifter.

Another object is to provide a new structure for a ferrite phase shifter capable of controlling phase shifting of RF energy at selected frequency bands.

A further object is the provision of an improved ferrite phase shifter capable of controllably varying the phase of RF energy at higher peak power than comparable prior art devices.

Yet a further object is to provide a new relatively small ferrite phase shifter characterized by relatively high peak and average power phase shifting capabilities of RF energy at selected frequency bands.

These and other objects of the invention are achieved by providing a ferrite phase shifter comprising a waveguide section through which RF energy in a selected frequency band of a selected mode can propagate, with a ferrite rod being centrally located in the waveguide section. The rod is encased in a novel structure of dielectric material which in addition to defining the location or position of the rod in the center of the waveguide section, is also used to provide dielectric loading of the rod to enhance the microwave performance as well as serving as a container of a coolant material used to control the temperature of the rod and thereby greatly increase the peak and average power capability of the phase shifter.

The encased ferrite rod itself is selected to be of a magnetic material with saturation magnetization characteristics comparable with the desired frequency of the operation and of a crystalline or grain structure which optimizes the peak power which the phase shifter can safely handle.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a pictorial view of the novel ferrite shifter of the present invention;

FIG. 2 is a longitudinal cross-sectional view of the phase shifter of FIG. 1;

FIG. 3 is a transverse cross-sectional view of the phase shifter o f FIG. 1;

FIG. 4 is a diagram useful in explaining the effect of dielectric gap loading on the performance of the phase shifter; and

FIGS. 5a and 5b are diagrams representing the saturation magnetization characteristics versus temperature of different materials used as the ferrite rods in phase shifters constructed in accordance with the teachings disclosed herein.

Reference is now made to FIGS. 1, 2 and 3 which are used to exemplify the structural characteristics of the ferrite phase shifter of the present invention. FIG. 1 is a pictorial view of a phase shifter 10, shown with exterior shielding walls 11 while FIG. 2 is a cross-sectional View of the phase shifter along lines 2 2 and FIG. 3 is a cross-sectional view along lines 33 (shown in FIG. 2). As seen from FIGS. 1 and 2, the phase shifter 10 includes a conventional waveguide section 12 having an interior 13 which is shown as having a rectangular cross-section formed by a pair of parallel broad walls 12a and a pair of parallel narrow walls 12b perpendicularly disposed with respect to the broad walls. The waveguide section 12 may include end flanges 12c for interconnecting the section to adjacent sections in the microwave system.

Within the section is located a ferrite rod 14 which is centrally positioned in the waveguide section, with the longitudinal axis of the rod being substantially aligned with the longitudinal axis of the section. Except for the ends 14a of rod 14, in one embodiment of the invention the rod is shaped as a bar having a rectangular cross-section as seen in FIG. 3. The rod is encapsulated or encased in a structure 15 which centrally supports the rod in the waveguide section 12 by means of the sides 15a thereof abutting against the inside surfaces of the walls 12a. Sides 15b of the encapsulating structure 15 abut the other sides of the bar-like rod 14 to provide dielectric loading thereto, as will be explained hereafter in detail.

The phase shifter also includes an inlet 21 and an outlet 22 which are integrally connected to the structure 15, to provide inlet and outlet paths for coolant material such as cooling liquid to be injected into the interior of the structure 15 and be removed therefrom respectively. As seen from FIG. 3, the exterior surface of the rod 14 is serrated so that the surface in a sense defines a plurality of longitudinal cavities 14b through which liquid injected through inlet 21 may flow over the surface of the rod 14 to be withdrawn from the structure 15 through outlet 22. Thus, even though the rod 14 is encased in the structure 15 the surface thereof is cooled by the flow of liquid between the inlet 21 and outlet 22. The phase shifter also includes a solenoid 25 wound about the exterior of waveguide section 12 for controlling the longitudinal magnetic field applied to the rod 14 and thereby Controlling the phase shift of the microwave or RF energy propagating through the section in a manner wellknown in the art.

Attention is now drawn specifically to the encasing structure 15. The structure is formed of a dielectric material which is advantageously sealed to be liquid-tight after the ferrite rod 14 is placed therein. The dielectric material is preferably one having a relatively low dielectric constant in order to optimize the change of phase which is achievable for a given value of magnetic field I applied to the ferrite rod. One dielectric material which has been found to be particularly advantageous is a fluorocarbon resin sold by the DuPont Corporation under the trademark Teflon 100 PEP, hereafter generally referred to as FEP Teflon. The FEP Teflon has a dielectric constant of approximately 2.1 and exhibits excellent heat sealing characteristics, so that after placing the ferrite rod 14 therein it can be folded and sealed to act as a liquid-tight container, enclosing the ferrite rod therein.

As is appreciated by those familiar with the art, when microwave energy in a particular mode, such as mode TE propagates through the phase shifter, its performance can be greatly enhanced by filling the gap between the ferrite rod 14 and the walls of the waveguide 12 with a dielectric material. However, it is also appreciated that the thickness of the material placed in these gaps affects the performance of the phase shifter. This phenomenon may better be explained in conjunction with FIG. 4 to which reference is made herein. The DC magnetic field in oersteds produced by direct current in the solenoid is diagrammed on the abscissa while the relative phase shift in degrees is plotted along the ordinate, with lines k through h designating different thicknesses or widths of the gaps between the ferrite rod 14 and the broad walls 12a. Line h represents a zero thickness, i.e. the sides of the ferrite rod are in contact with the interior surfaces of the broad walls 12a, while line k represents an optimum gap thickness filled by the dielectric material. The actual optimum thickness will depend on the relative width and height dimension of the waveguide section and the ferrite rod centrally located therein. As seen from FIGS. 2' and 3 sides 15a of structure 15 are used to fill the gaps between the rod and the sections broad walls. Thus, sides 15:: of dielectric structure 15, in addition to forming the liquid-tight container together with sides 15b, also serve as gap filling dielectric material to optimize the phase shifters operation.

Just as sides 15a of structure 15 perform a dual function as hereinbefore descirbed, sides 15b of the same structure also fulfill two functions. One function of sides 15b is to comprise a part of the liquid-tight container in which the ferrite rod 14 is encased as hereinbefore described, while the other function of sides 15b is to provide dielectric side loading of the ferrite rod. As is appreciated by those familiar with the art, proper dielectric side loading improves the phase shifting characteristic of the device. The thickness of sides 15b need be controlled so that the sides are thick enough to draw the energy to the center of the waveguide through the ferrite rod, but not too thick in order not to produce mismatching with the rod.

From the foregoing, it is thus seen that the structure 15 of the dielectric material in a sense fulfills three functions. One is to encase the rod in a liquid-tight container so that liquid injected through inlet'21 may flow around the serrated surface of rod 14 to control its temperature, with the liquid being expelled from the interior of structure 15 through the outlet 22. Another function that structure 15 fulfills is providing a dielectric material between the rod and the broad walls 12a to fill the gaps therebetween, while sides 15b of the structure provide dielectric side loading for the ferrite rod. In accordance with the teachings of the present invention, a cooling liquid of dielectric material is used to control the temperature of the ferrite rod. One cooling liquid which has been found to be particularly advantageous is an inert fluoro chemical liquid which has a dielectric constant of 1.91 at three kilomegacycles per second (kmc.). It is appreciated, however, that any other cooling liquid of dielectric material of a low dielectric constant may be used in the novel phase shifter of the present invention.

The significance of cooling and thereby controlling the temperature of the ferrite rod becomes apparent when considering the temperature sensitivities of the magnetic materials from which ferrite rod, for use in ferrite phase shifters are produced at present. For example, FIGS. 5a and 5b are diagrams of the saturation moment or magnetization versus temperature characteristics of two different materials which are presently used to form ferrite rods for ferrite phase shifters. FIG. 5a: represents the saturation characteristics of an yttrium-gadoliniumiron garnet material, while FIG. 5b represents the saturation magnetization versus temperature characteristics of a magnesium-manganese ferrite material. As is seen from the two figures, the change in saturation magnetization as a function of change in temperature differs for each of the materials. However, irrespective of the difference between the materials, both are sensitive to changes in temperature.

Therefore, when ferrite rods used in ferrite phase shifters are made of such materials, without controlling the rods temperature, the phase shifter is quite temperature-sensitive. In prior art phase shifters, to alleviate this problem, i.e. minimize the change in temperature of the ferrite rods,the maximum average power deliverable by the ferrite phase shifter was held to a minimum at which the rods temperature could be regarded as relatively constant. However, in accordance with the teachings of the present invention as by employing the novel structure 15 which in essence serves as a liquid-tight container in which the ferrite rod is embedded and by using a cooling liquid of dielectric material flowing between inlet 21 and outlet 22 about the serrated surface of the rod 14, the temperature of the rod can be accurately controlled by removing the heat dissipated therein. Thus the maximum average power which the phase shifter can deliver is greatly increased.

The novel phase shifter of the present invention, in addition to providing high average power, is also characterized by high peak power which is achieved by the careful selection of the crystalline or grain characteristics of the ferrite rod 14. To achieve the high peak power, it has been found that the material chosen for the rod should be one capable of increasing the level where the onset of ferromagnetic limiting begins. Ferromagnetic limiting is believed to be caused by a phenomenon known as spin wave propagation. The spin waves exist within the ferromagnetic medium with the spin dipoles being the mechanism for sustaining wave motion. Normally the spin waves are quite small; however, at a critical power level, known as the threshold limiting point, the waves grow abnormally large. At this point, large amounts of RF energy are transferred to the crystal lattice and are dissipated as heat. Thus, in order to provide high peak power without high insertion loss. It is necessary to m-.

crease the threshold limiting point of the ferrite rod.

It has been found that the threshold limiting point can be increased successfully by decreasing the crystal grain size of the rodmaterial. The small grain size tends to form boundaries in the rod material to provide sufficient discontinuities therein and thereby break up the spin waves. It has been found that as the grain boundaries are reduced, the spin wave spectrum is in turn reduced and the threshold limiting point increases. Substantial improvements of peak power handling have been achived by reducing the crystal grain size. Thus, in achereinbefore described cordance with the teachings of the present invention, the ferrite rod is produced from a small grain size material to greatly increase the maximum peak power which the phase shifter is capable of delivering.

In addition to controlling the crystalline or grain characteristics of the rods material, the shapes of the rods ends 14a (FIG. 2) often referred to as the input and output transitions, are optimally shaped to maximize the amount of phase shift which the phase shifter is capable of providing. Although substantial phase shifting has been accomplished with various type of transitions, including dielectric quarter wave, dielectric multiple step, wedge tapers parallel to either the E or H planes as well as multiple steps parallel to either of said planes, the best results were obtained with transitions comprising pyramid shaped taper where propagation of the desired TE mode is enhanced.

There has accordingly been shown and described herein a novel ferrite phase shifter in which the ferrite rod conventionally centrally located in a wavegide section is encased or encapsulated in a dielectric material formed as a liquid-tight container through which a cooling material such as a dielectric cooling liquid flows about the rod to control its temperature and thereby optimize the average peak power deliverable by the device. The encasing dielectric material also serves to support the rod in its central position, as well as provide dielectric side loading and gap filling dielectric material in the gaps between the rod and the broad walls of the waveguide section, thereby maximizing the phase shifting characteristics of the novel device. The peak power deliverable is optimized by controlling the grain size of the material of which the ferrite rod is manufactured.

The teachings of the invention have been employed in constructing ferrite phase shifters operating in different RF bands. The structural and performance characteristics of the phase shifter reduced to practice are presented for exemplary purposes in the following table.

Frequency Band C S Waveguide Section Dimensions, inches:

Width:

.394 0. 750 .510 0.975 Length 4. 8. 00 Total Rod Length (with tapered ends), inches 6. 00 13. 00

Rod Material Rod Grain Size, microns 6 Encasing Material (Structure FEP Teflon FEP Teflon Dielectric Constant of 15"--. 2. 1 2.1 Thickness of Sides 15a, inch 0.050 112 Thickness of Sides 15b, inch. 0. 049 150 Cooling Liquid 3M FX-78 3M FX-78 Dielectric Constant oi Cooling Liquid. 1. 91 1. 91 Peak Power, kw 115 60 0. 9 1. 0

Insertion Loss (at peak power), dbl--. Average Power, watts 700 700 Phase Shift Range (degrees) Range of) B.C. Magnetic F 1 Yttrium-Gadolinium-Iron Garnet. 2 Magnesium-Manganese Ferrite.

It should be appreciated that the invention is not limited to the two specific ferrite phase shifters, the characteristics of which have been listed by way of example rather than as a limitation on the teachings of the invention. It should further be appreciated that modifications may be made by those familiar with the art without departing from the true spirit of the invention. Therefore, all such modifications and equivalents are deemed to fall within the scope of the invention as claimed in the appended claims.

What is claimed is:

1. In a phase shifter of the type including a waveguide section and a ferrite rod centrally located therein for providing controllable phase shifting of microwave energy propagating through said waveguide section as a function of a magnetic field applied to said rod, the improvement comprising:

dielectric encasing means disposed within said waveguide section and encasing said ferrite rod; the surface of said rod being serrated to provide a plurality of cavity-like means between said encasing means and said rod; and

inlet and outlet means communicating with said encasing means, said inlet and outlet means being adapted to provide a path for a dielectric liquid coolant flow through said cavity-like means.

2. A ferrite phase shifter comprising:

a rectangular wavegnide section for controlling the propagation of microwave energy therethrough;

a ferrite rod centrally mounted within said section with the longitudinal axis aligned with the longitudinal axis of said section;

a liquid-tight container of dielectric material centrally mounted in said waveguide section and contacting portions of said rod over a major longitudinal length thereof, said liquid-tight container further including inlet and outlet means for providing paths for liquid to flow into and from said liquid-tight container;

a cooling liquid having dielectric characteristics flowing in said liquid-tight container between said inlet and outlet means for cooling the ferrite rod located therein; and

means for applying a controllable longitudinal magnetic field to said encased rod to shift the microwave energy propagating through said waveguide section as a function of the magnetic field.

3. The ferrite phase shifter of claim 2 wherein the surface of said rod is serrated to provide paths for said cooling liquid to flow from said inlet to said outlet means at least about the surface of said rod.

4. The ferrite phase shifter of claim 3 wherein said liquid-tight container defines an exterior surface, a portion of which is in contact with said waveguide section for centrally positioning said ferrite rod in said section, and for providing dielectric loading thereof.

5. The ferrite phase shifter of claim 4 wherein said waveguide section and said rod have substantially rectangular cross-section in directions perpendicular to their longitudinal axes and said liquid-tight container comprises four sides about said rod, two opposite sides being in contact with adjacent sides of said waveguide section to centrally support said rod therein and provide dielectric material in the gaps between said rod and said sides of said waveguide section.

6. In a ferrite phase shifter of the type including a waveguide section, a ferrite rod centrally disposed therein and means for controlling the magnetic field about said ferrite rod to control the phase shifting of the energy propagating through said waveguide section the improvement comprising:

a liquid-tight structure of dielectric material disposed within said waveguide section and contacting portions of said rod over a major longitudinal length thereof, said structure having at least a portion thereof in contact with said waveguide section for centrally disposing said ferrite rod in said waveguide section and for providing dielectric loading of preselected gaps between said rod and said waveguide section;

cooling-material inlet and outlet means integrally coupled to said structure; and

a cooling material having dielectric characteristics flowing in said structure about said rod between said inlet and outlet means for controlling the temperature of said rod.

7. The ferrite phase shifter of claim 6 wherein said structure is liquid-tight and said cooling material is a dielectric cooling liquid, said rod having a serrated surface for providing paths for the cooling liquid to flow thereabout and control the temperature thereof.

8. The ferrite phase shifter of claim 7 wherein said Waveguide section includes a first pair of parallel broad walls and a second pair of parallel walls perpendicular with respect to said broad walls and said rod is barshaped, said first portion of said structure filling the gaps between said bar-shaped rod and said broad walls with the dielectric material thereof, and a second portion 10 of said structure of dielectric material, providing dielectric side loading of said rod.

8 References Cited UNITED STATES PATENTS 3,001,151 9/1961 Morris 333-4243 X 5 3,217,272 11/1965 Russell 33'3-l.1 X

HERMAN KARL SAALBACH, Primary Examiner.

P. L. GENSLER, Assistant Examiner. 

1. IN A PHASE SHIFTER OF THE TYPE INCLUDING A WAVEGUIDE SECTION AND A FERRITE ROD CENTRALLY LOCATED THEREIN FOR PROVIDING CONTROLLABLE PHASE SHIFTING OF MICROWAVE ENERGY PROPAGATING THROUGH SAID WAVEGUIDE SECTION AS A FUNCTION OF A MAGNETIC FIELD APPLIED TO SAID ROD, THE IMPROVEMENT COMPRISING: DIELECTRIC ENCASING MEANS DISPOSED WITHIN SAID WAVEGUIDE SECTION AND ENCASING SAID FERRITE ROD; THE SURFACE OF SAID ROD BEING SERRATED TO PROVIDE A PLURALITY OF CAVITY-LIKE MEANS BETWEEN SAID ENCASING MEANS AND SAID ROD; AND INLET AND OUTLET MEANS COMMUNICATING WITH SAID ENCASING MEANS, SAID INLET AND OUTLET MEANS BEING ADAPTED TO PROVIDE A PATH FOR A DIELECTRIC LIQUID COOLANT FLOW THROUGH SAID CAVITY-LIKE MEANS. 